Abstract

We determine the relative branching fractions of semileptonic B decays to charmed final states. The measurement is performed on the recoil from a fully reconstructed B meson in a sample of 362x10(6) B (B) over bar pairs collected at the Upsilon(4S) resonance with the BABAR detector. A simultaneous fit to a set of discriminating variables is performed on a sample of (B) over bar -> DXl(-) (v) over bar center dot decays to determine the contributions from the different channels. We measure Gamma(B--> Dl(-)(v)over bar>l)/Gamma(B--> DXl(-)(v) over barl)=0.227 +/- 0.014 +/- 0.016, Gamma(B--> D(*)l (v) over barl)/Gamma(B--> DXl(-)(v) over barl)=0.582 +/- 0.018 +/- 0.030, and Gamma(B--> D(**)l(-)(v) over barl)/Gamma(B--> DXl(-)(v) over barl)=0.191 +/- 0.013 +/- 0.019 for the charged B sample, and Gamma((B) over bar (0)-> Dl(-)(v) over barl)/Gamma((B) over bar (0)-> DXl(-)(v) over barl)=0.215 +/- 0.016 +/- 0.013, Gamma((B) over bar (0)-> D(*)l(-)(v) over barl)/Gamma((B) over bar (0)-> DXl(-)(v) over barl)=0.537 +/- 0.031 +/- 0.036, and Gamma((B) over barB(0)-> D(**)l(-)(v) over barl)/Gamma((B) over bar (0)-> DXl(-)(v) over barl)=0.248 +/- 0.032 +/- 0.030 for the neutral B sample, where uncertainties are statistical and systematic, respectively.